The invention relates to a driver circuitry, and in particular, to the driver circuitry which provides high speed variable output power and high performance operation within a wide dynamic range.
Output power drivers have found numerous applications in telecommunications, microelectronics and other hi-technology industries. In fiber optics industry, for example, such drivers are widely used for direct modulation of lasers and optical modulators. Driver circuits designed for fiber optics applications must satisfy certain requirements, including operability in a controlled impedance environment, capability to deliver variable output power and provide a pre-determined output waveform within a wide dynamic range of power. Moreover, high level of circuit integration and demand for high speed operation impose an additional requirement for the driver circuitry to operate at a low voltage supply while maintaining other characteristics of the circuitry.
Unfortunately, existing laser driver circuits provide an optimum performance over a narrow range of the output power which doesn""t guarantee sufficient quality of an optical eye output and requires high voltage supply to maintain the quality of the waveform at the required level. As a result, existing circuit designs are not compatible with high level of integration, high speed and low power requirements.
Accordingly, there is a need to develop a driver circuitry which would provide a high performance operation over a wide dynamic range of the output power.
It is therefore an object of the invention to provide a driver circuitry which would avoid the afore-mentioned problems.
According to one aspect of the invention there is provided a driver circuit, comprising an output stage having a first differential amplifier whose operating point is controlled by a first control signal. Preferably, the differential amplifier is a cascode amplifier. The circuit may further comprise a pre-driver stage having a second differential amplifier, the pre-driver stage being responsive to an input signal and generating an output pre-driver signal to be received by the output stage of the driver. Preferably, the operating point of the second differential amplifier is controlled by a second control signal. It is arranged that the operating points of the first and second differential amplifiers are controlled in such a manner that higher output power of the driver corresponds to the higher output pre-driver signal. Conveniently, the first and second control signals are generated by the same control unit. If required, it may be arranged that the generated signals are identical. The control unit is operating in response to a reference signal, e.g. variable DC voltage or a feedback signal supplied from the output of the driver. Alternatively, the feedback signal may be signal may be supplied from the output of the device being controlled by the driver circuit, e.g. from the output of a laser or an optical modulator. Beneficially, the driver circuit is monolithically integrated with a device to be driven by the circuit.
According to another aspect of the invention there is provided a driver circuit, comprising a pre-driver stage having a differential amplifier whose operating point is controlled in such a manner that higher output power of the driver corresponds to the higher output signal from the pre-driver.
According to another aspect of the invention there is provided a pre-driver stage for a driver circuit, the pre-driver stage providing a preliminary amplification of an input signal and comprising a differential amplifier whose operating point is controlled in such a manner that higher output power of the driver corresponds to the higher output signal from the pre-driver.
According to one more aspect of the invention there is provided a driver circuit, comprising:
a power control unit;
a pre-driver stage and an output stage;
the power control unit being responsive to a reference signal and generating first and second control signals;
the pre-driver stage comprising a second differential amplifier and being responsive to an input signal and the second control signal and generating an output pre-driver signal, the output pre-driver signal being a preliminary amplified input signal;
the output stage comprising a first differential amplifier and being responsive to the output pre-driver signal and the first control signal and generating the output driver signal;
the first and second control signals controlling operating points of the first and second differential amplifiers respectively.
Control of the operating points of the first and second differential amplifiers is provided in such a manner that higher output power of the driver corresponds to the higher output pre-driver signal.
According to yet another aspect of the invention there is provided a method of operating a driver circuit, the circuit comprising an output stage having a first differential amplifier and a pre-driver stage having a second differential amplifier, the pre-driver being responsive to an input signal and generating an output pre-driver signal to be received by the output stage,
the method comprising controlling of operating points of the output stage and the pre-driver stage in such a manner that higher output power of the driver corresponds to the higher output signal from the pre-driver.
Additionally, the method may comprise the step of controlling operating points of the output stage and the pre-driver stage by first and second control signals, the signals being identical.
The proposed architecture of the driver circuit provides an extended dynamic range of the output power of the driver and improved waveform quality of the output signal.